Magnetostrictive resonant-disc test jig



July 28, 1959 M- S. BANN AL MAGNETOSTRICTIVE RESONANT-DISC TEST JIGFiled April 1, 1957 3 Sheets-Sheet 1 MICHAEL HERBERT BY INVENTORS S.vBANN O. LEWIS AT TORNEYS July 28, "1959 M. s. BANN ETAL 2,897,439

' MAGNETOSTRICTIVE RESONANTQDISC TEST-JIG Filed April 1, 1957 I 5Sheets-Sheet 2 INVENTORS MICHAEL S- BANN HERBERT O. LEW!S I MMMMATTORNEYS M. S.BANN ETAL 2,897,439 YMAGNETOSTRICTIVE RESONANT-DISC TESTJIG Filed April 1, 1957 July 28; 1959 3 Sheets-Sheet 3 FREQ.

METER FREQ; ACUUM TUBE GEM VOLTMETER INVENTORS MICHAEL S. BANN HERBERTO. LEWIS ATTORNEYS This invention relates to apparatus for testing thefrequency response of magnetostrictive discs.

Cylindrical discs of magnetostrictive material are used in themanufacture of mechanical filters. of the type described and claimed inPatent No. 2,6l5,981,titled Electromechanical Filter, and Patent No.2,717,361, titled Mechanical Filter, both to Melvin L. Doelz. The discsin such filters must be tuned precisely to .a given frequency. Often,all of the discs used in a filter are tuned to the same frequency withband pass requirements determined by the diameter of coupling wires. Inother cases, the discs are tuned to different frequencies to givevarying types of frequency responses. In any case, it is essential thatdiscs used in the construction of such filters be tuned to precise givenfrequenciesv This invention provides convenient means for measuring thefrequency response of magnetostrictive discs and excites each disc in .asymmetrical mode, that is used in parallel-disc mechanical filters. Theinvention permits rapid alignment of a filter disc between a pair ofcoils received on opposite sides ofthe disc with an initial magnetizingsurge automatically provided upon insertion of the disc. An oscillatoryelectromagnetic field is then provided that symmetrically excites thedisc. One coil excites the disc by magnetostrictive action, and theother coil has an electromotive force induced in it by inversemagnetostrictiveaction of the disc. Shielding housings of non-permeableconducting materialare provided about the coils to prevent stray fluxfrom. by-passing the disc. The invention permits a visearrangementwherein discs of various thicknesses can be tested.

Further objects, features and advantages of .this invention will beapparent to a personskilled in the art upon further study of thespecification and drawings, in which:

Figure 1 is a partial isometric view having exploded portions;

Figure 2 is a partially-sectioned side-elevational view of theinvention;

Figure 3 is a front elevational view; and,

Figure 4 is a blockdiagram of a circuit in which the invention can beused.

Now referring to the invention in more detaiLFigure 1 illustrates itwith an isometric view, which, is partially exploded and which ispartially sectionedfor clarity. It includes a base .10 and a back member11 fixed uprightly along one edge of the basejltl. A pair, of, pins 12and 13 are fixed toback memberlland extend parallel to each other andtobase 10. An adjustable support ,16.is formed with a pair of openings 17and 18, shown.in Figure 3, that slideably receive pins 12 and 13,respectively. An adjustment screw21 having a knurled knob 2'4 isreceived slideably through adjustable support 16, but has a shoulder 23thatengages adjustable support 16 on its outer side. Screw 21 isreceived threadedly through back member 11. A leaf spring 22 (shown inFigure 2) .is positioned between back member 11 and adjustablesupport 16to bias them apart, whereby adjustable support 16 is forcedlagainstshoulder 23. i V V i 2 Thus, adjustable support 16 maintains spring 22in a conventional vise arrangement by means of .the support pins andadjustment screw.

Patented July 28, 1959 Furthermore, r piv ting rod 26 an as op .rod.27

are each fixed at one ,endtoback member 1.1. .Adjustable supportIdaho-happenings 28 and ,291thatslide ably receive both of these rods,which further provide support for adjustable support 16.

.A disc holder 31 has ani p ni g 2 form dthreue it which receivespivoting rod 26. The other side of disc holder 31 is formed with a notch34. Disc holder 31 is pivotablea-bout rod 26,; but its pivoting movement.islimited in the downwarddirectioniniFigure 1 when .notch 34 engagesstop rod 27. ,Holderfil is formed centrally with a V-shaped groove 36that is rounded on its bottom to receive a ,magnetostrietivedisc .37,,which is the work-piece of the jig An L-shaped bracket 41 is-fixed tothe edges of base 10 and back member {11. A Surgeinitiating switch 42 isfastened to bracket riland has ajplunger-actuating pin 43 extendingupwardlyin-Figure 1. Switch ,42 ,isi-of h normally-open momentarywtypwherein :i is close only during the period thatpin 43 is depressed, but

.is self-opening when pressureis removed from pin 43.

A connect r 4 .isa so supported by braeket-d ,',andla pair of leads.47and A8 serially connect the contacts ,of

switch 42 to therespective output terminals of 6011116010 46. Connector4 6 is ve0 1111e :ta,ble to a transient ,directcurrent source (notshow-n).

A p of h ldin housing r 1 andela ereceired and Supported in r pe eopeangshrough back :member 11 and adjustable support,16,,. tnd;are 1ixedtherein by a pair of set screws 53 and 54. Theshielding housng are m eof non-p rmeab e cond c ing material such as brass, and eachisformedwith a flared end 56 or 57, w h is ount su e nt th -inn r surfaces ofback memberll oradjustable support; 1j6, respectively. Coil forms-5 8and 59 are respectively ICCfiiVQdz-Wilhin shielding housings-'51 and,52

Each coil 61 or 62 is positioned near theend of;;its

coil form .518 or 59, with its leads received through grooves cutin thecoil'form. -A pair ,of coaxial connectors 63 and are respectively fixedto theouter ends of,shieldingr hou sings5131x1 52. They connect to theea o the respe iv ,eils- Connectors 6.3 and v64 provi he si n e mina f rth r A coil cover .66 .or-,67 is mounted :everiheend. of h el inehous g:aeiugt su to tr e dis and coils 61 ,and-fi2are adjacent therespeetive'coil covers. However, the flared ends of the housingsand the coilcovershaves. larger diameter {than -the,disc

being tested. .Coil cover 66 is aflush .yvi'th .the inner surface.ofback member 11; and the other coilcover 67 is flush-with the innersurface of;a c;lj-ustable,-.support 16. The coil covers are made ofinsulating material, and they are constructed witha thickness thatflis,as small as the structural-rigidity of its material permits, such .asof .an inch. -Its thickness is notcritical.

The spacing between back member llandadiustable support 1,6 isdeterminedby the thickness of the magnetostrictive discs to be tested.The spacingprovides suflicient clearance to enable-the discsto.be-easily injected and rejected by the pivoting movement :of. .discholder ,31.

When a disc is placed inthe jig, notch-34 of disc holder 31 is receivedagainst stop-rod 27, where the disc holder engages actuating pin 43 toclose the contacts of surge switch-42. i u

Fig. 4--shows a circuit in which the invention can be used. However,other circuits ean alsousethe invention such as that in'the Fa tentApplication No. 644,838 filed March 18,, 1957, and titledMagnetostrictive Disclose oscillator by Herbert 0..; I .ewis..Blocki70;.in..F,.igure,4 schematically representsjthe invention,with;disc.37 received between coils 61 and 62. Surge switch 42 isconnected to a B plus supply through a resistor 93 and one terminal ofconnector 46. A pair of adjustable capacitors 71 and 72 are connectedrespectively across coils 61 and 62 through connectors 63 and 64,respectively. Each adjustable capacitor has an end connected to ground.

The other side of surge switch 42 is connected to the other terminal ofconnector 46, which is connected to the grids of a pair of gas dischargetubes 76 and 77. A first discharge capacitor 78 is connected between theplate of discharge tube 76 and the ungrounded side of adjustablecapacitor 71. Similarly, a second discharge capacitor 79 is connectedbetween the plate of the other discharge tube 77 and the ungrounded sideof second adjustable capacitor 72. Each gas tube has its cathode biasedbelow cut-off by a voltage divider comprising resistors 96 and 97,because the control grids are normally maintained at ground potential bygrid leak resistors 98.

The thyratron cathodes are maintained at fixed positive potentials bythe associated voltage dividers and by-pass capacitors 99. The platesare normally maintained at B plus potential by the associated chargingresistors Capacitors 7 8 and 79 are thus normally charged to B pluspotential. The control grids of the thyratrons are normally maintainedat ground potential by the grid return resistors. The thyratrons arethus maintained in a nonconducting state by virtue of the cathode bias.

Thus, when a magnetostrictive disc is initially placed into theinvention, switch 42 is closed; and a large transient direct-currentsurge is provided through coils 61 and 62 by the firing of dischargetubes 76 and 77 through their respective discharge capacitors.

At the instant switch 42 is closed the grids are brought to a potentialmore positive than the cathodes, causing the tubes to conduct. The platevoltages immediately descend to approximately the cathode potentials,placing a voltage across coils 61 and 62, which is slightly less thanthe B plus potential. Capacitors 73 and 79 then discharge through coils61 and 62 for a period of about one millisecond, magnetizing thesurfaces of the disc. When the plate currents reach some very low valuethe tuba become non-conductive, at which time, capacitors 78 and 79begin to recharge to B plus potential.

The current surges through the respective coils cause a permanentmagnetization of the magnetostrictive material on opposite surfaces ofthe disc. This permanent magnetization enables proper magnetostrictivetransducing without additional permanent magnets and without additionalwindings that receive direct-current to provide a DC. flux.

A frequency generator 81 and frequency meter 82 are connected to theungrounded side of variable capacitor 71, and a vacuum-tube voltmeter 83is connected to the ungrounded side of second variable capacitor 72.

Capacitors 71 and 72 are adjusted so that they parallel resonate withcoils 61 and 62, respectively, at nearly the frequency of themagnetostrictive discs to be tested. These parallel-resonant circuits,91 and 92, however, are broadband and have nearly a flat response overthat portion of the spectrum where the active response of any disc 37exists.

The frequency generator is swept through a frequency range that includesthe main frequency response of the disc being tested, and the responseis noted by means of the vacuum-tube voltmeter 83.

Of course, spectrum analyzers utilizing cathode ray tubes or recordingdevices may be utilized instead of frequency generator 81, meter 82 andvacuum-tube voltmeter 83, as will be apparent to one skilled in the artafter studying this specification.

Although this invention has been described with respect to a particularembodiment thereof, it is not to be so limited as changes andmodifications may be made therein which are within the full intendedscope of the invention as defined by the appended claims. M

We claim:

1. Apparatus for testing the resonant frequency of a magnetostrictivecylindrical disc comprising a base member, a pair of upright memberssupported on said base, said upright members having inner surfacesparallel to each other, a pair of housings made of non-permeableconducting material received through said upright members respectively,said housings being axially aligned, a pair of cover members providedover the ends of said housings flush with the respective inner surfacesof said upright supports, a pair of coils respectively received in saidhousings adjacent to the respective housing covers, said coils beingaxially aligned, a disc support formed with a V-shaped groove, apivoting rod received between said upright members, said disc supportpivotable on said pivoting rod, and a stop rod received between saidupright supports, with said disc support supporting saidmagnetostrictive disc in its V-shaped groove in axial alignment withsaid coils with said disc support engaging said stop rod.

2. Apparatus as defined in claim 1 having a pair of variable capacitorsrespectively connected across said coils to form respectiveparallel-resonant circuits tuned to a frequency near the resonantfrequency of said magnetostrictive disc.

3. Apparatus as defined in claim 2 having a momentary switch beingsupported on said base, a direct-voltage source connected to one end ofsaid switch, said switch being closed by engagement by said disc supportwith said magnetostrictive disc in test position, a pair of gasdischarge tubes, and a pair of discharge capacitors, and said gasdischarge tubes and said discharge capacitors being connectedrespectively in series between said parallel-resonant circuits and theother side of said surge switch.

4. Apparatus for testing a magnetostrictive cylindrical disc comprisinga base, a back member fixed uprightly to said base, an adjustableupright member, a pair of pins fixed to said back member and slideablyreceived through openings in said adjustable member to support it withrespect to said base, an adjustment screw received through said backmember and adjustable support to enable adjustment of the spacingbetween them, a pair of cylindrical housings made of non-permeableconducting mate-- rial, one of said housings received through said backmember, the other of said housings received through said adjustablemember in axial alignment with said one hous ing, a pair of coil formsreceived in said housings respectively, a pair of coils wound about saidcoil forms respectively, a pair of coil covers respectively receivedover the ends of said housings flush with the inner surface of said backmember and adjustable support respectively, respective coils provided onsaid coil forms near the inner ends of said housings, a pivoting pin anda stop pin received on opposite sides of said housings between said backmezn ber and adjustable member, a disc support formed Wind a V-shapedgroove and pivotably supported on one side oi its groove by saidpivoting rod, the pivoting movement of said disc support being limitedby said stop rod, the magnetostrictive disc receivable in said groovefor being aligned axially with said coils when said disc support cngagessaid stop rod, a switch being supported with respect to said base, andan actuating member being provided with said switch and being engageablewith said disc support as it engages said stop rod.

References Cited in the file of this patent UNITED STATES PATENTS2,234,456 Schaurte et al Mar. ll, 1941 2,334,393 Dillon NOV. 16, 19432,537,753 Hansen Jan. 9, 1951 2,574,795 Miller Nov. 13, 1951 2,587,664Stout Mar. 4, 1952 2,642,482 Segsworth June 16, 1953

